1. Field of the Invention
The present invention relates generally to a single poly electrical erasable programmable read only memory (EEPROM), and more specifically to a single poly electrical erasable programmable read only memory (EEPROM) including two tunnel dielectric parts.
2. Description of the Prior Art
An EEPROM (electrically erasable programmable read only memory) provides excellent performance. Thanks to voltages required for programming and erasing being self-generated, only an external source is required for operation. Programming and erasing is carried out in each memory cell for recording a bit data. Charges can be trapped in a floating gate and thus the characteristic of each memory cell can be changed to store data bit “0” or data bit “1”. Each memory cell consists of two MOS transistors, wherein one storage transistor having a floating gate is used for trapping charges while the other access transistor is used for operation. Proper bias voltages are applied while programming and erasing the EEPROM (electrically erasable programmable read only memory). For instance, while the EEPROM (electrically erasable programmable read only memory) is erased, charges are injected into the floating gate, and the transistor stores a data bit “1”; while the EEPROM (electrically erasable programmable read only memory) is programmed, charges are removed from the floating gate, and the transistor stores a data bit “0”.
For programming and erasing the EEPROM (electrically erasable programmable read only memory), a tunneling dielectric layer must be disposed between a substrate and the floating gate, thereby charges being trapped in or removed from the floating gate through the tunneling dielectric layer while applying proper bias voltages. Thus, the structure, the material and the charge tunneling frequency of the tunneling dielectric layer affect life time of the EEPROM (electrically erasable programmable read only memory). Specifically, these properties affect life time of the EEPROM (electrically erasable programmable read only memory) in a high temperature atmosphere.